Rho Ophiuchi nebulosity. Optical image of nebulosity in the region of the star Rho Ophiuchi (purple, just above centre). North is at top. This star is swathed in purple nebulosity, the reflection nebula IC 4604, in which dust particles reflect the star's light. The bright star Antares (Alpha Scorpii, red) is also seen. To the right of this star is the bright globular cluster M4 (NGC 6121, pink), with the star Sigma Scorpii (purple) above it. Sigma Scorpii is surrounded by an emission nebula, which glows as its gas is excited by the star's radiation. Dark lanes of dust are seen at upper centre, obscuring the light of the dense starfields in this region.